1. Field of the Invention
The present invention relates to a satellite navigation system comprising a server and on-vehicle navigating terminals communicably connected to the server via a communication network, wherein map data supplied to the navigating terminals are partially updateable.
2. Description of Related Art
In recent years, a satellite navigation system has become popular. The satellite navigation system guides a user (driver) to a user""s desired destination with a map shown on a navigating terminal. A practical configuration of such satellite navigation system is configured as now described. In response to a user""s request, map data stored in a server placed at a map data base site are transmitted to such a navigating terminal as an on-vehicle navigation unit, mobile navigation unit, PDA (personal digital assistants), or mobile phone, through communication means. The communication means is composed of for example a computer network (e.g., the Internet) or a mobile communication network. The navigating terminal includes a GPS (global-positioning system) to detect a vehicle""s current position, and provides a map on a monitor thereof using both the vehicle""s current position and the received map data.
Such a satellite navigation system is advantageous in that it is able to enable each navigating terminal (i.e., a user) to make reference to the newest versions of maps. In order to gain the advantage, a user has to have the newest map data by reloading map data stored in a block in the navigating terminal, whatever the map data handled in the server is updated.
Practically, in each navigating terminal participating in the satellite navigation system, all the map data in one block should be downloaded to renew the map data when the map data is updated in the server.
However, in the conventional satellite navigation system, even when a unit of map data is partially updated in the server, the entire map data in each block should be downloaded due to the above downloading way on the one-block basis. As a result, amounts of data to be reloaded become extremely large, resulting in that a communication load imposed on a communication line becomes high as well. This necessitates a longer time to process map data in the reloading operation and a high communication cost.
The present invention has been made in view of the above circumstances. An object of the present invention is, therefore, to greatly reduce an amount of data to be re-loaded so that a load imposed on a communication line can be lowered when map data is updated.
The present invention is reduced into practice in various aspects, such as a server incorporated in a satellite navigation system, a terminal in the system, and a method of updating map data in the system.
In order to achieve the above object, as one aspect of the present invention, there is provided a method of updating map data in a satellite navigation system comprising a server storing the map data to be used by a navigating terminal to perform navigation; the method comprising the steps of: causing the server to produce the map data divided into a plurality of sets of map data that are mutually-independent set by set; causing the server to transmit, to the navigating terminal, information including a set of updated map data; and causing the navigating terminal to use the received set of updated map data to update map data temporarily stored in the navigating terminal for the navigation.
Further, it is preferred that the information to be transmitted from the server to the terminal includes information indicating a type of operation to be carried out by the terminal for the update.
As a result, in the server, the map data can be updated partially, that is, every set of divided data map, in an easier manner. This partially updateable configuration is also effective in reloading map data from the server to each navigating terminal. For reloading the map data, it is sufficient that only one or more sets of map data that has been updated are delivered from the server to the navigating terminal. Hence an amount of map data to be downloaded can be reduced greatly. Each navigating terminal is therefore able to update, set by set, map data temporarily stored for navigation by using both of only the received set of map data and the operation of a specified type. Therefore, for updating the map data used in each navigating terminal, a communication load imposed on the communication means can be lessened noticeably.
Further, because the map data are divided into a plurality of sets independent of each other, each certain set of map data can be replaceable with no effect on the other sets of map data in terms of data connections.
According to another aspect of the present invention, there is provided a server for storing map data to be supplied to a terminal for performing navigation, both of the server and the terminal being incorporated in a satellite navigation system, the server comprising: a storage for storing the map data divided into a plurality of sets of map data that are mutually-independent set by set; an updating unit configured to update, every set of the divided map data, the map data stored in the server; and a transmitting unit configured to transmit, to the navigating terminal, information including a set of updated map data.
As a result, when the map data used in each navigating terminal is updated, a communication load imposed on the communication means can be lessened noticeably, because it is enough that only a set of map data that has been updated is transmitted from the server to each navigating terminal via the communication means.
It is also preferred that the information to be transmitted from the server to the terminal includes information indicating a type of operation to be carried out by the terminal for the update. This transmission enables each navigating terminal to perform more complicated updating operations in an easier way.
By way of example, the type of operation to be carried out by the terminal is one selected from a group of processes including replacing the entire map data with new data, partially replacing the map data by new data, partially deleting map data from the map data, and partially adding new map data to the map data, the partially replacing, partially deleting, and partially adding operations being carried out set by set.
It is also preferred that the map data consists of different kinds of map data formed into a layered structure of map data. Practically, as one example, the layered structure of map data includes a first layer formed by data of a plurality of objects, a second layer formed by a plurality of blocks, each block consisting of one or more objects of the same kind, and a third layer formed by a plurality of layers, each layer consisting of data of a plurality of blocks for the same type of depiction of map data. For example, each set of the map data is composed of one of each layer of map data, each block of map data, and each object of map data.
The above layered structure of map data makes it easier to divide entire map data into a plurality of sets of map data classified according to their natures.
Still, according to another aspect of the present invention, a recording medium for storing map data is provided, which is incorporated in a server of a satellite navigation system, the map data being divided into a plurality of sets of map data that are mutually-independent set by set, updateable every set of the divided map data, and configured to have different kinds of map data formed into a layered structure of map data, wherein the layered structure of map data includes a first layer formed by data of a plurality of objects, a second layer formed by a plurality of blocks, each block consisting of one or more objects of the same kind, and a third layer formed by a plurality of layers, each layer consisting of data of a plurality of blocks for the same type of depiction of map data. By using this recording medium, the server is able to provide a configuration in which map data for navigation can be updated partially.
Still, according to another aspect of the present invention, there is provided a navigating terminal for performing navigation based on map data supplied from a server through communication means, both of the server and the terminal being incorporated in a satellite navigation system, the navigating terminal comprising: a receiving unit configured to receive, from the terminal though the communication means, information including a set of updated map data and selected from the map data divided into a plurality of sets of map data that are mutually-independent set by set; an updating unit configured to update map data temporarily stored in the terminal for the navigation, by using the received information including the set of updated map data.
Preferably, the information to be received from the server includes information indicating a type of operation to be carried out by the terminal for the update. It is also preferred that the type of operation to be carried out by the terminal is one selected from a group of processes including replacing the entire map data with new data, partially replacing the map data by new data, partially deleting map data from the map data, and partially adding new map data to the map data, the partially replacing, partially deleting, and partially adding operations being carried out set by set.
It is therefore enough for each navigating terminal to update the stored map data using only one or more received sets of map data. An amount of data that is involved in the update processing is reduced largely compared to the conventional. A load to calculate data by each navigating terminal diminishes as well, thus making the update faster and reducing a cost of the update.